1. Field of the Invention
The present invention relates to a LED driver controller, and more particularly to a LED driver controller capable of providing power factor correction and zero current switching for LED lighting applications.
2. Description of the Related Art
In a LED lighting application utilizing an AC power source, the load current for a LED module has to be regulated to not only provide a stable lighting but also protect the LED module.
FIG. 1 illustrates a prior art LED driver circuit. As illustrated in FIG. 1, the LED driver circuit, powered by a line voltage VDC, a DC voltage, includes a LED driver controller 100, an NMOS transistor 101, an inductor 102, a diode 103, a resistor 104, a capacitor 105, and a LED module 110.
The LED driver controller 100, biased by VDC, is used to generate a gating signal VG in response to a current sensing signal VCS in a way that the duty ratio of the gating signal VG becomes larger/smaller as the current sensing signal VCS goes down/up.
The NMOS transistor 101 is driven by the gating signal VG to control the power conversion of the LED driver circuit.
The inductor 102 is used to store a magnetic energy when the NMOS transistor 101 is on, and the diode 103 is used to release the magnetic energy to the LED module 110 when the NMOS transistor 101 is off.
The resistor 104 is used to generate the current sensing signal VCS according to a load current IL.
The capacitor 105, a filtering capacitor, is used in cooperation with a full-wave rectifier (not illustrated in FIG. 1) to provide the DC voltage VDC.
When in operation, the peak of the load current IL will be regulated at a constant value and the LED module 110 will thereby produce a regulated illumination.
However, there are some disadvantages in the prior art LED driver circuit. First, as the AC component of a full-wave rectified voltage output from a full-wave rectifier is filtered out by the capacitor 105, there is no way to perform power factor correction therein. Second, as the LED driver controller 100 cannot get the information of the end time of the discharging of the inductor 102, it cannot perform soft switching on the NMOS transistor 101 and this can cause EMI problem.
In view of the disadvantages of the prior art LED driver circuit, the present invention proposes a novel LED driver controller for a LED driver circuit, which can perform not only power factor correction but also zero current switching when regulating the current of a LED module.